Bioeconomic Modeling of an Imported Disease in California Lettuce

We develop a theoretical and empirical model to measure the benefits and costs of
policy options for controlling a seedborne, imported fungus, Verticillium dahliae, seriously
affecting lettuce production in California. In 1995, the disease Verticillium wilt, caused
by the fungus V. dahliae, unexpectedly appeared in a lettuce crop in Watsonville, Santa
Cruz County. Since then, the disease has spread rapidly through the Parajo Valley, the
prime lettuce production region of California. Plant pathologists have determined spinach
seeds to be the primary pathway by which the fungus is introduced to the soil (Atallah
et al., 2010). Once introduced, the pathogen persists in the soil for many years, affecting
subsequent crops. We develop a simulation model to describe growers' profit maximizing
decisions regarding which crops to plant, the timing of the plantings, and efforts to control
the disease. We also estimate a structural econometric model explaining crop choice decisions
made by growers in Monterey County. A simulation model allows for the incorporation of
biological parameters estimated from the work of plant pathologists. In addition, we can
compare different scenarios, in particular those that growers are hesitant to implement in
their fields without knowing the impacts.